Tandem-type hot-wire velocity meter probe

ABSTRACT

An improved tandem-type hot-wire velocity meter probe for the measurement of flow velocity of liquids and/or gases, comprising two hot-wire members disposed in tandem at upstream and downstream ends of an insulating support member placed in the flow path (e.g., a pipe or a conduit) of the fluid under measurement. The upstream or leading end hot-wire member has its downstream or trailing side buried or otherwise concealed in the insulating support member, while the downstream-end hot-wire member has its upstream side similarly buried or otherwise concealed therein, so that the exposed surfaces of the two hotwire members indicate a difference between their rates of heat transfer to the fluid in proportion to the flow rate thereof. This difference can be obtained in terms of a difference in electrical resistance between the hot-wire members by means of a meter incorporated in a bridge circuit including the hot-wire members. There are also disclosed herein several examples of the improved flowmeter probe all conforming to the above basic configuration of the two hot-wire members and the support member.

United States Patent Hayakawa 14 1 July 18,1972

[54] TANDEM-TYPE HOT-WIRE VELOCITY METER PROBE [72] Inventor: Hldeolhyakawa, Yokohama, Japan [73] Assignee: Yugen Kahlil Tsukm Soltken,Tokyo,

Japan [22] Filed: April 8, 1970 211 Appl. No.: 26,638

Primary Examiner-Richard C. Queisser Assistant Examiner-C. E. Snee, IllAttorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT An improvedtandem-type hot-wire velocity meter probe for the measurement of flowvelocity of liquids and/or gases, comprising two hot-wire membersdisposed in tandem at upstream and downstream ends of an insulatingsupport member placed in the flow path (e.g., a pipe or a conduit) ofthe fluid under measurement. The upstream or leading end hot-wire memberhas its downstream or trailing side buried or otherwise concealed in theinsulating support member, while the downstreamend hot-wire member hasits upstream side similarly buried or otherwise concealed therein, sothat the exposed surfaces of the two hot-wire members indicate a difference between their rates of heat transfer to the fluid in proportionto the flow rate thereof. This difierence can be obtained in terms of adifference in electrical resistance between the hot-wire members bymeans of a meter incorporated in a bridge circuit including the hot-wiremembers. There are also disclosed herein several examples of theimproved flowmeter probe all conforming to the above basic configurationof the two hot-wire members and the support member.

6 China, 7 Drawing Figures PATENTEuJuuamz 3, 77' 0 5 FIG.|(C)

TANDEM-TYPE HOT-WIRE VELOCITY METER PROBE BACKGROUND OF THE INVENTIONThis invention relates to an improved velocity meter probe. 5

More specifically, the invention relates to an improved tandem-typehot-wire velocity meter probe for the electrothermic measurement of flowvelocity of liquids and/or gases (hereinafter referred to by thegeneralized term fluid) by means of hot-wire members in tandemarrangement.

An electrothermic measuring instrument analogous, but no doubt inferior,to the present invention has already found a widespread use inanemometry. Called the hot-wire anemometer, it is now used extensivelyfor the measurement of the velocity of a steady flow of air or a gas. Inprinciple, the hot-wire anemometer is designed to measure the velocityof air or a gas in terms of a change in the temperature, obtainedthrough a change in the electrical resistance, of a single electricallyheated wire (i.e., the hot wire) as it is cooled in the fluid undermeasurement.

The transfer of heat to the fluid from the hot wire placed thereinconsists of the twofold process of (l) the heating by the hot wire ofthe portion of the fluid surrounding it and (2) the carrying away of theheated portion by the flow. Stated illustratively, the hot wire in thefluid produces a consistent surrounding layer of the heated portion(hereinafter referred to simply asheated boundary layer). The thicknessof this heated boundary layer is subject to change in accordance withthe flow velocity of the fluid, becoming less with increase in the flowvelocity.

The heated boundary layer mentioned above has a great influence upon theresponse characteristics of hot-wire velocity meters in general. Thatis, in the event the flow speed is reduced or even decreased to zero,the heated boundary layer around the hot wire shows a correspondingincrease in thickness as above and thus causes a time lag in the speedat which the velocity meter responds to the change in the flow velocity.This time lag is the length of time needed for the hot wire to form anew heated boundary layer of the fluid therearound and depends on theheat capacity and/or viscosity coefficient of the fluid and otherfactors.

Hence, the thickened layer around the hot wire, as a result of the moreor less reduced flow velocity of the fluid, impairs the responsecharacteristics of the meter to fluctuations in the flow velocity,especially when the velocity stepwisely becomes zero. Furthermore, whenthe flow velocity is decreased, the velocity meter becomes inordinatelysensitive to the slightest relative displacements of its hot wire andthe fluid, such as those caused by mechanical or acoustical vibrations,thus giving rise to errors in measurement.

The conventional hot-wire velocity meter possesses another seriousdrawback in that it is unable to sense the direction of the flow in theevent of rapid, intermittent fluctuations in the flow velocity of thefluid. This drawback is all the more serious because, even when thevelocity of flow as measured in a given cross section of an adequateflow path (e.g., a tube or a conduit) of the fluid becomes rapidly zero,a localized flow thereof is still present in the path. The result isthat the conventional velocity meter probe, with provision made for onlyone hot wire, is incapable of measuring exact flow velocities of a fluidin the cross section of its flow path.

SUMMARY OF THE INVENTION All of the above deficiencies accompanying theconventional hot-wire velocity meters, as typified by the hot-wireanemometer, are successfully overcome by the present invention which, infact, affords a distinct improvement in electrotherrnic measurement.

It is thus a primary object of the invention to provide an improvedhot-wire velocity meter probe incorporating two hotwire members intandem arrangement for the measurement of flow velocities of liquidsand/or gases from a difference in the heat transfer rate therebetween.

Another object of the invention is to provide an improved hot-wirevelocity meter probe which manifests a highly dependable responsecharacteristic even when the fluid under measurement is flowingconsiderably slowly, since the undesirable effects of the heatedboundary layers produced by the two hot-wire members are nullified byvirtue of counterac tion therebetween.

Still another object of the invention is to provide an improved hot-wirevelocity meter probe capable of highly exact measurement of flowvelocities of a fluid even assuming relative displacements between thefluid and the hot-wire members due to mechanical or acousticalvibrations, since these vibrations, too, are counterbalanced as they actcommonly upon both of the two hot-wire members.

A further object of the invention is to provide an improved hot-wirevelocity meter probe capable of sensing the direction of flow besidesmeasuring the flow velocities in a cross section of an adequate flowpath (e.g., a tube or a conduit) even when the flow velocity decreasesstepwisely rapidly down to zero.

An additional object of the invention is to provide an improved hot-wirevelocity meter probe whereby the flow velocity of a fluid withconsidrable irregular fluctuations can be measured both accurately andspeedily.

These and the various ancillary objects as well as the novel featuresthat are considered characteristic of the invention will become moreapparent and understandable from the following detailed description ofcurrently preferred embodiments thereof when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIGS. 1 (A), (B), (C), (D) and (E) are cross-sectional views showingpreferred embodiments of the invention;

FIG. 2 is an explanatory connection diagram, illustrated by way ofexample only, of the tandem-type hot-wire velocity meter probe of theinvention; and

FIG. 3 is an explanatory diagram showing a mode of transfer of heat froma cylindrical solid body to a fluid in which it is placed.

DETAILED DESCRIPTION OF THE INVENTION The most characteristic feature ofthe tandem-type hot-wire velocity meter probe of the invention resides,of course, in the use of two hot-wire members in tandem arrangement,i.e., at upstream and downstream ends of an approximately flat shapedsupport member made of an electrically and thermally insulatingmaterial.

Referring now to the drawings, FIG. 1(A) through FIG. 1(E), inclusive,illustrate five preferred embodiments of the invention all conforming tothe above fundamental constitution. In FIG. 1(A), slots 3a and 3b arerespectively formed in the middle of an upstream or leading end 2a and adownstream or trailing end 3b of a support member 2, which is forexample made of glass, the slots 3a and 3b being formed to such a depththat approximately half the cross section of hotwire members or hotelongated members la and 1b are respectively buried therein. Thehot-wire members la and lb are further bonded in the slots 3a and 3b.

Also in FIG. 1(B), slots 20 and 2d of such a depth that hotwire membersla and lb are buried nearly completely therein are formed in the middleof the upstream end 2a and downstream end 2b of the support member 2.The hot-wire members 1a and lb are respectively buried in the slots 2cand 2d, with adequate exposure permitted therefrom, in such a mannerthat both the upstream end 2a and downstream end 2b of the supportmember 2 offer scarcely any protrusions of the hot-wire members la and1b buried therein.

FIG. 1(C) illustrates still another example of the velocity meter probeof the invention, wherein a paste like insulating substance, forexample, enamel or lacquer, is solidified integrally with hot-wiremembers 10 and 1b placed on both sides thereof in parallel with eachother.

FIG. 1(D) illustrates yet another example, wherein tapes 2e and 2f of anadequate width which are made of an electric conductor are bonded to theupstream and downstream ends 2a and 2b of the support member 2.

Yet a further example is shown in FIG. 1(E), wherein films 2g and 2h ofan electric conductor are formed at the upstream and downstream ends 2aand 2b of the support member by the process of vacuum deposition.

The probe as above described may be used with its two hotwire members Inand 1b forming two arms of a bridge circuit incorporating a meter M asillustrated in FIG. 2, the meter M aflording reading of a difference inelectrical resistance between the wires, The meter pointer will stand ata standstill with the flow speed at zero, deflecting in proportionthereto.

The operation of the tandem-type hot-wire velocity meter probe of theinvention, having the above described fundamental constitution, will nowbe described hereinbelow.

Generally, the upstream side and downstream side of an object placed ina flow of a fluid show different rates of heat transfer (Nusseltsnumber) to the fluid therefrom, the difference therebetween increasingwith increase in the flow velocity of the fluid. Now, let it be assumedthat the velocity meter probe illustrated in FIG. 1(A), is placed in afluid flowing in a direction in conformity with the upstream" anddownstream designations of the probe ends. Only the upstream half of thecircumferential surface of the hot-wire member 1a buried at the upstreamend 2a of the support member 2 is in contact with the fluid, thustransferring heat thereto, whereas the downstream half of thecircumferential surface of the hot-wire member In is concealed in thesupport member 2 so that there is no transfer of heat to the fluidtherefrom. On the other hand, only the downstream half of thecircumferential surface of the hot-wire member lb at the downstream end2b of the support member 2 is in contact with the fluid, thus alsotransferring heat thereto, while the upstream half thereof is similarlyconcealed in the support member 2 so that heat is not transferred to thefluid therefrom.

As a result, the hot-wire member la and the hot-wire member lb transferheat to the fluid at difierent rates.

A corresponding difference in electrical resistance therebetween can beobtained by means of a meter (M) connected as illustrated in FIG. 2between the hot-wire members.

To elaborate further upon the above phenomenon, suppose that acylindrical solid body 1c approximating in cross-sectional shape to thehot-wire members la and lb is placed in a flow of a fluid as in FIG. 3,in which is shown the distribution pattern of the rate of imagined heattransfer from the body to the fluid. The flow at the upstream side 1dthereof is forced apart so that the flow velocity is increased there. Atthe downstream side 1e of the body 1c, on the other hand, where thefluid tends to stand stagnant, the flow velocity is low. Hence, the rateof transfer of heat from the body 1c is different at everycircumferential point thereof, being high at the upstream side 1d andlow at the downstream side 1e.

The above phenomenon is effectively utilized by the present invention,wherein the two hot-wire members are disposed in tandem arrangement insuch a manner that the downstream half of the circumferential surface ofthe upstream-end hotwire member In and and upstream half of thecircumferential surface of the downstream-end hot-wire member lb areburied in the support member 2 made of insulating material.Consequently, in contrast to the conventional single-hot-wire probe thathas measured the flow velocity from an average heat transfer rate overthe whole circumferential surface of the single hot wire, the inventionmakes it possible to achieve a more exact, rapid measurement of the flowspeed on the basis of a difference in the heat transfer rate between theexposed upstream half of the hot-wire member 1a and the exposeddownstream half of the hot-wire member lb.

Althouth the invention has been described hereinbefore with respect tothe measurement of flow speed, it will be understood that the velocitymeter may be used as a flowrate meter with equal effectiveness.

I claim: 1. In a tandem-type hot-wire velocity meter probe comprisingtwo hot elongated members disposed respectively upstream and downstreamof a fluid flow of which the velocity is to be measured, and meanslocated interrnediately of said two elongated members, the improvementwherein said means comprises a support member for said elongatedmembers, said support member being made of insulating material andhaving an essentially elliptical cross-sectional configuration, the endsof the major axis of said ellipse defining respectively rounded upstreamand downstream ends of said support member in the path of said fluidflow, each of said hot elongated members being almost entirely buriedin, respectively, said rounded upstream and downstream ends to form thesubstantially smooth outer surfaces of said ends, said elongated membersand said support member being rigidly interconnected with each other.

2. The velocity meter probe as claimed in claim 1, wherein saidelongated members are in the form of wires or rods and respectivelyburied more or less in slots formed in the middle of the upstream endand downstream end of said support member.

3. The velocity meter probe as claimed in claim 1, wherein said supportmember is in the form of a paste-like insulating substance, which issolidified integrally with said elongated members on both sides.

4. The velocity meter probe as claimed in claim 1, wherein saidelongated members are in the form of tapes of an adequate width whichare made of an electric conductor, said tapes being bonded respectivelyto the upstream and downstream ends of said support member.

5. The velocity meter probe as claimed in claim 1, wherein saidelongated members are films of an electric conductor material formed byvacuum deposition.

6. The velocity meter probe as claimed in claim 1, wherein saidelongated members form arms of a bridge circuit incorporating a meterwhich is adapted to indicate the difference in electrical resistancebetween said elongated members which corresponds to said difference inthe heat transfer rate therebetween.

1. In a tandem-type hot-wire velocity meter probe comprising two hotelongated members disposed respectively upstream and downstream of afluid flow of which the velocity is to be measured, and means locatedintermediately of said two elongated members, the improvement whereinsaid means comprises a support member for said elongated members, saidsupport member being made of insulating material and having anessentially elliptical cross-sectional configuration, the ends of themajor axis of said ellipse defining respectively rounded upstream anddownstream ends of said support member in the path of said fluid flow,each of said hot elongated members being almost entirely buried in,respectively, said rounded upstream and downstream ends to form thesubstantially smooth outer surfaces of said ends, said elongated membersand said support member being rigidly interconnected with each other. 2.The velocity meter probe as claimed in claim 1, wherein said elongatedmembers are in the form of wires or rods and respectively buried more orless in slots formed in the middle of the upstream end and downstreamend of said support member.
 3. The velocity meter probe as claimed inclaim 1, wherein said support member is in the form of a paste-likeinsulating substance, which is solidified integrally with said elongatedmembers on both sides.
 4. The velocity meter probe as claimed in claim1, wherein said elongated members are in the form of tapes of anadequate width which are made of an electric conductor, said tapes beingbonded respectively to the upstream and downstream ends of said supportmember.
 5. The velocity meter probe as claimed in claim 1, wherein saidelongated members are films of an electric conductor material formed byvacuum deposition.
 6. The velocity meter probe As claimed in claim 1,wherein said elongated members form arms of a bridge circuitincorporating a meter which is adapted to indicate the difference inelectrical resistance between said elongated members which correspondsto said difference in the heat transfer rate therebetween.